The present invention relates to a fluid heating or cooling system. More particularly, the present invention relates to a control circuit for determining the level of contents in a tank in a water heating system. Even more particularly, the present invention relates to a control circuit having a dry bowl sensing circuit for a coffee brewer system.
Fluid heating systems generally include a tank and a heater. The tank is filled with a liquid to be heated. Liquid is often removed from the tank as the liquid is heated. As the tank becomes empty, the remaining liquid, heater, and tank become hotter much more quickly. In order to prevent the heater and tank from overheating, or to prevent unnecessary use of the heater, liquid heating Systems often include liquid level sensors which determine when the tank is empty.
Water heating systems utilized in coffee brewing machines include a tank in thermal communication with a heater. Water is heated in the tank, and the water level in the tank decreases as water drips out an exit port. When the tank is empty (a dry bowl condition), the heater should be turned off to protect the heater and tank.
Prior art coffee brewers utilized costly fluid sensors disposed in the tank to determine the amount of water in the tank. Other prior art coffee brewers utilize a timing technique which assumes that the tank is empty after a particular amount of time and turns the heater off. However, this technique is unable to compensate for ambient conditions and clogged conduits which can affect the amount of time to empty the tank. Thus, this technique is disadvantageous because the coffee brewer may be turned off prematurely when the tank still contains water or too late when the tank is empty.
It would therefore be advantageous to have an inexpensive apparatus for accurately determining whether a tank in a water heater system is empty.